ldexp.c

seed傅立叶变换程序

/****************************************************************************/
/*  LDEXP  v3.70                                                           */
/*  Copyright (c) 1993-2001 Texas Instruments Incorporated                  */
/****************************************************************************/
#include <math.h>
#include <errno.h>

double ldexp(double x, int exp)
{
     int *ptr = (int *)&x;
     long texp = (long) exp + ((ptr[0] >> 7) & 0xFF);

     /***********************************************************************/
     /* IF RESULT UNDERFLOWS, RETURN 0.0.  IF RESULT OVERFLOWS, RETURN      */
     /* +- INFINITY.                                                        */
     /***********************************************************************/
     if      (texp < 1)      
       x = 0.0; 
     else if (texp > 0xFE) 
     { 
       errno = ERANGE;
       x = (x < 0) ? -HUGE_VAL : HUGE_VAL;
     }
     else                   
       ptr[0] = (ptr[0] & 0x807F) | ((int)texp << 7);
   
     return x;
}